There are several different ways of configuring electric motors each of which has its own associated advantages and disadvantages. Many of these configurations provide very efficient operations. However, this high efficiency is generally restricted to a particular optimum operating frequency of the motor and when the motor moves away from this operating frequency the efficiency may drop dramatically. In order to address this problem, motors of the prior art have been operated in conjunction with gearing systems, such that they can drive axles at different speeds, while still operating close to their own optimum rotation frequency. The provision of gears adds cost to the system and can themselves reduce efficiency.
One known type of motor is the universal motor which is schematically shown in FIG. 1 and has a rotor component and stator component that both have winding arrangements. Such a universal motor can be operated with either DC or AC power and generally provides a compact and high powered motor. To some extent, a universal motor can be viewed as combining the advantages of both induction motors and permanent magnet motors. However, the difficulties associated with coupling the required waveforms to the rotor winding arrangements have significant drawbacks. This problem is addressed in U.S. Pat. No. 8,450,954.
Although such a universal motor may provide a compact and high powered motor, the efficiency of such a motor still reduces dramatically away from an optimum operating frequency and thus, such a motor is generally operated in conjunction with some gearing mechanism.